Polyester fibers, their production and their use

ABSTRACT

Described are fibers comprising aliphatic-aromatic polyester and non-layered platelet-shaped particles selected from the group of inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides and carbides, having a thickness in the range from 20 nm to not more than 100 nm and an aspect ratio of not more than 20:1. The polyester fibers possess excellent bending fatigue resistance, give distinctly reduced abrasion and are useful for producing screens or other industrial fabrics.

CLAIM FOR PRIORITY

This application is based upon German Patent Application No. DE 10 2005033 350.8, entitled “Polyesterfasern, Verfahren zu deren Herstellung undderen Verwendung”, filed Jul. 16, 2005. The priority of German PatentApplication No. DE 10 2005 033 350.8 is hereby claimed and itsdisclosure incorporated herein by reference.

TECHNICAL FIELD

The present invention concerns polyester fibers having abrasion and highbending fatigue resistance, especially monofilaments useful in screensor conveyor belts for example.

BACKGROUND OF INVENTION

It is known that polyester fibers, especially monofilaments forindustrial applications, are in most cases subjected to high mechanicaland/or thermal stressors in use. In addition, there are in many casesstressors due to chemical and other ambient influences, to which thematerial has to offer adequate resistance. As well as adequateresistance to all these stressors, the material has to possess gooddimensional stability and constancy of its stress-strain properties oververy long use periods.

One example of industrial applications imposing the combination of highmechanical, thermal and chemical stresses is the use of monofilaments infilters, screens or as conveyor belts. This use requires a monofilamentmaterial possessing excellent mechanical properties, such as highinitial modulus, breaking strength, knot strength and loop strength andalso high abrasion resistance coupled with a high hydrolysis resistancein order that it may withstand high stresses encountered in its use andin order that the screens or conveyor belts may have an adequate uselife.

Molding compositions possessing high chemical and physical resistanceand their use for fiber production are known. Polyesters are widely usedmaterials for this purpose. It is also known to combine these polymerswith other materials, for example in order to achieve a specific degreeof abrasion resistance.

Industrial manufacturers, such as paper makers or processors, utilizefilters or conveyor belts in operations taking place at elevatedtemperatures and in hot moist environments. Polyester-based manufacturedfibers have a proven record of good performance in such environments,but when used in hot moist environments polyesters are vulnerable tomechanical abrasion as well as hydrolytic degradation.

Abrasion can have a wide variety of causes in industrial uses. Forinstance, the sheet-forming wire screen in papermaking machines is inthe process of dewatering the paper slurry pulled over suction boxes,and this results in enhanced wear of the wire screen. At the dry end ofthe papermaking machine, wire screen wear occurs as a consequence ofspeed differences between the paper web and the wire screen surface andbetween the wire screen surface and the surface of the drying drums.Fabric wear due to abrasion also occurs in other industrial fabrics, forinstance in transportation belts due to dragging across stationarysurfaces, in filter fabrics due to the mechanical cleaning and in screenprinting fabrics due to the movement of a squeegee across the screensurface.

Adding fillers to improve the mechanical properties of fibers is knownper se.

GB-A-759,374 describes the production of artificial fibers and filmshaving improved mechanical properties. The claimed process ischaracterized by the use of very finely divided metal oxides in the formof aerosols. The particle size shall be not more than 150 nm. Viscose,polyacrylonitrile and polyamides are mentioned as examples of polymers.

EP-A-1,186,628 discloses a polyester raw material comprising finelydispersed silica gels. The individual particles have diameters of up to60 nm and aggregates, if present, are not more than 5 μm in size. Thefiller is said to lead to polyester fibers having improved mechanicalproperties, improved color and improved handleability. The reference isunforthcoming about applications for these polyester fibers.

U.S. Pat. No. 6,544,644 (which corresponds to WO-A-01/02,629) describesmonofilaments useful, inter alia, in papermaking machines. Thedescription part refers mainly to polyamide monofilaments; polyester rawmaterials are also mentioned in very general terms. The monofilamentsdescribed are characterized by the presence of nanoscale inorganicmaterials. These provide enhanced resistance to abrasion. Platelets aredescribed as well as spherical particles. The non-spherical particlesdescribed are nanoclays, i.e., layered particles. These can be treatedwith swelling agents, such as phosphonium or ammonium compounds, so thatthe layered assemblies wholly or partly dissolve to form particles lessthan 10 nm thick in one dimension. In the case of platelet-shapedparticles, this reference thus mentions either the use of layeredparticles whose layered structure has only incompletely dissolved, if atall, so that aggregates below 100 nm in thickness are present, or whoselayered structure has completely dissolved, in which case particleshaving thicknesses below 10 nm are present. Exfoliated montmorillonitesare mentioned in this reference as one example of these platelets.

The use of layer-shaped and platelet-shaped nanoparticles, so-callednanoclays, in polyester spinning dopes has shown that in general, thereare problems with the spinning. Either the spinning dopes cannot beprocessed at all, or special measures have to be taken if a fiber is tobe produced at all. If, on the other hand, nanoparticles lackingsufficient thickness are used, it has been determined that the fibersformed do not have satisfactory textile-technological properties. It isbelieved that the high fraction of interfaces due to these very smallparticles in the polymer has a disruptive effect on the drawing stage,so that polymer chains are insufficiently aligned after the drawingoperation. This has an adverse effect on the mechanical properties, forexample the strength, of the fiber.

The use of nanoscale fillers can lead to fibers having improvedmechanical properties. In general, however, the addition of fillersleads not only to the desired improvement in some properties but at thesame time also to a deterioration in others.

It has now been found that, surprisingly, selected polyester rawmaterials comprising certain nanoscale fillers possess distinctlyimproved abrasion resistance compared with unmodified polyester rawmaterials without their dynamic fatigue resistance, expressed by thebending fatigue resistance, being significantly reduced by the use of afiller; in fact, it may even be increased. This performance profile wasobserved on selected polyester raw materials.

Proceeding from this prior art, the present invention has for its objectto provide filled polyester fibers which, as well as excellent abrasionresistance, possess dynamic fatigue resistances which are equivalent toor even superior than those of unfilled polyester fibers.

The present invention further has for its object to provide transparentfibers having high abrasion resistance and excellent dynamic fatigueresistance.

SUMMARY OF INVENTION

This invention provides fibers comprising aliphatic-aromatic polyesterand non-layered platelet-shaped particles selected from the group ofinorganic oxides, hydroxides, carbonates, bicarbonates, nitrides andcarbides, having a thickness in the range from 20 nm to not more than100 nm and an aspect ratio of not more than 20:1.

DETAILED DESCRIPTION

The invention is described in detail below with reference to severalembodiments and numerous examples. Such discussion is for purposes ofillustration only. Modifications to particular examples within thespirit and scope of the present invention, set forth in the appendedclaims, will be readily apparent to one of skill in the art. Terminologyused herein is given its ordinary meaning consistent with the exemplarydefinitions set forth immediately below.

Thickness, as used herein, refers to the smallest extension of theparticle along one of its main axes of inertia.

Aspect ratio, as used herein, is the quotient along the largestextension of the particle along one of the main axes of inertia to thesmallest extension of the particle along one of the main axes ofinertia; that is, the aspect ratio is the quotient formed from thelargest length of the particle (along one of the main axes of inertia)to the thickness of the particle.

Preference is given to polyester fibers having a free carboxyl groupcontent of not more than 3 meq/kg.

These polyester fibers comprise an agent to cap free carboxyl groups,for example a carbodiimide and/or an epoxy compound.

Polyester fibers thus endowed are stabilized to hydrolytic degradationand are particularly suitable for use in hot moist environments,especially in papermaking machines or as filters.

Any fiber-forming polyester can be used as long as it comprisesaliphatic and aromatic groups and is formable in the melt. Aliphaticgroups are herein also to be understood as meaning cycloaliphaticgroups.

These thermoplastic polyesters are known per se. Examples thereof arepolybutylene terephthalate, polycyclohexanedimethyl terephthalate,polyethylene naphthalate or especially polyethylene terephthalate.Building blocks of fiber-forming polyesters are preferably diols anddicarboxylic acids or appropriately constructed oxyl carboxylic acids.The main acid constituent of polyesters is terephthalic acid orcyclohexanedicarboxylic acid, but other aromatic and/or aliphatic orcycloaliphatic dicarboxylic acids may be suitable as well, preferablypara- or trans-disposed aromatic compounds, for example2,6-naphthalenedicarboxylic acid or 4,4′-biphenyldicarboxylic acid, andalso isophthalic acid. Aliphatic dicarboxylic acids, such as adipic acidor sebacic acid for example, are preferably used in combination witharomatic dicarboxylic acids.

Useful dihydric alcohols typically include aliphatic and/orcycloaliphatic diols, for example ethylene glycol, propanediol,1,4-butanediol, 1,4-cyclohexanedimethanol or mixtures thereof.Preference is given to aliphatic diols which have two to four carbonatoms, especially ethylene glycol; preference is further given tocycloaliphatic diols, such as 1,4-cyclohexanedimethanol.

Preference is given to using polyesters comprising structural repeatunits derived from an aromatic dicarboxylic acid and an aliphatic and/orcycloaliphatic diol.

Preferred thermoplastic polyesters are especially selected from thegroup consisting of polyethylene terephthalate, polyethylenenaphthalate, polybutylene naphthalate, polypropylene terephthalate,polybutylene terephthalate, polycyclohexanedimethanol terephthalate, ora copolycondensate comprising polybutylene glycol, terephthalic acid andnaphthalenedicarboxylic acid units.

The polyesters used according to the present invention typically havesolution viscosities (IV values) of not less than 0.60 dl/g, preferablyof 0.60 to 1.05 dl/g and more preferably of 0.62-0.93 dl/g (measured at25° C. in dichloroacetic acid (DCE)).

The nanoscale fillers used according to the present invention endowpolyester fibers with excellent abrasion resistance without adverselyaffecting the dynamic properties, expressed by the bending fatigueresistance.

The fillers used according to the present invention are specificnon-layered platelet-shaped particles. These are selected from the groupconsisting of inorganic oxides, hydroxides, carbonates, bicarbonates,nitrides and carbides.

A further characteristic property of these fillers is their shape. Theparticles are not spherical but platelet shaped. Their thickness is notmore than 100 nm, preferably not more than 80 nm and in particular inthe range from 20 to 60 nm. A further characteristic property of thesefillers is their aspect ratio, i.e., the ratio of the largest extensionof the particle on one of the main axes of inertia to the smallestextension of the particle along one of the main axes of inertia. Theaspect ratio is not more than 20:1. Layered fillers, such asphyllosilicates (so-called nanoclays), montmorillonites for example, arenot wanted in this invention, since their use not only disrupts theprocessing of the fibers but also did not lead to any significantimprovement in properties being observed.

Typically, the nanoscale non-spherical oxides used according to thepresent invention are oxides of metals of group IIa of the periodictable, preferably oxides of magnesium, of calcium or of strontium, oroxides of metals of group IIIb of the periodic table, preferably oxidesof aluminum, of gallium or of indium, or oxides of metals of group IVaof the periodic table, preferably oxides of titanium, of zirconium or ofhafnium, or oxides of metals of group IIIa of the periodic table,preferably oxides of scandium or of yttrium or oxides of metals orsemimetals of group IVb of the periodic table, preferably oxides ofsilicon, of germanium or of tin.

Instead of oxides, the corresponding hydroxides can also be used, orelse mixed crystals formed from different metal oxides, for exampleAl₂O₃*2SiO₂ (mullite).

Typically, the nanoscale non-spherical carbonates used according to thepresent invention are carbonates of metals of group IIa of the periodictable, preferably carbonates of magnesium, of calcium or of strontium.

Typically, the nanoscale non-spherical carbides used according to thepresent invention are carbides of metals of group IIIb of the periodictable, preferably carbides of aluminum, of gallium or of indium, orcarbides of metals or semimetals of group IVb of the periodic table,preferably carbides of silicon, of germanium or of tin.

Typically, the nanoscale non-spherical nitrides used according to thepresent invention are nitrides of metals of group IIIb of the periodictable, preferably nitrides of aluminum, of gallium or of indium, ornitrides of metals or semimetals of group IVb of the periodic table,preferably nitrides of silicon, of germanium or of tin.

Particular preference is given to using nanoscale non-spherical aluminumoxide, aluminum nitride, silicon dioxide, zirconium dioxide, siliconcarbide, silicon nitride, yttrium oxide or calcium carbonate.

Very particular preference is given to using nanoscale non-sphericalaluminum oxide or calcium carbonate.

The polyester raw materials filled and needed to produce the fibers ofthe present invention can be produced in various ways. For instance,polyester and filler, and also if appropriate further additives, can bemixed in a mixing assembly, for example in an extruder, by melting thepolyester, and the composition is then fed directly to the spinneret dieor the composition is granulated and spun in a separate step. The pelletobtained may, if appropriate, also be spun as a masterbatch togetherwith additional polyester. It is also possible to add the nanoscalefillers before or during the polycondensation of the polyester.

Suitable nanoscale non-spherical fillers are commercially obtainable.For example, the DP 6096 product (calcium carbonate in ethylene glycol)from Nano Technologies, Inc., Ashland, Mass., USA can be used.

The level of nanoscale non-spherical filler in the fiber of the presentinvention can vary within wide limits, but is typically not more than 5%by weight, based on the mass of the fiber. The level of nanoscalespherical filler is preferably in the range from 0.1% to 2.5% by weightand in particular in the range from 0.5% to 2.0% by weight.

The identities and amounts of the components a) and b) are preferablychosen so that transparent products are obtained. Unlike polyamides, thepolyesters used according to the present invention are notable fortransparency. It has been determined that, surprisingly, the nanoscalenon-spherical fillers have no adverse effect on transparency. Bycontrast, the addition of just about 0.3% by weight of non-nanoscaletitanium dioxide (delusterant) causes the fiber to turn completelywhite.

It has further been determined that, surprisingly, the abrasionresistance of the fibers according to the present invention can be stillfurther enhanced by the addition of polycarbonate. The amount ofpolycarbonate is typically up to 5% by weight, preferably in the rangefrom 0.1% to 5.0% by weight and more preferably in the range from 0.5%to 2.0% by weight, based on the total mass of the polymers.

Fibers are in the context of this description to be understood asmeaning any desired fibers.

Examples thereof are filaments or staple fibers which consist of aplurality of individual fibers, but are monofilaments in particular.

The polyester fibers of the present invention can be produced byconventional processes.

The present invention also provides a process for producing theabove-defined fibers, the process comprising the measures of:

-   -   i) mixing polyester pellet with non-layered platelet-shaped        particles selected from the group of inorganic oxides,        hydroxides, carbonates, bicarbonates, nitrides and carbides        having a thickness in the range from 20 nm to not more than 100        nm and an aspect ratio of not more than 20:1,    -   ii) extruding the mixture comprising polyester and non-layered        platelet-shaped particles through a spinneret die,    -   iii) withdrawing the resulting filament, and    -   iv) optionally drawing and/or relaxing the resulting filament.        The present invention also provides a process for producing the        above-defined fibers, the process comprising the measures of:    -   i) feeding an extruder with polyester pellet mixed before or        during the polycondensation with polyester pellet with        non-layered platelet-shaped particles selected from the group of        inorganic oxides, hydroxides, carbonates, bicarbonates, nitrides        and carbides, having a thickness in the range from 20 nm to not        more than 100 nm and an aspect ratio of not more than 20:1,    -   ii) extruding the mixture comprising polyester and non-layered        and platelet-shaped particles through a spinneret die,    -   iii) withdrawing the resulting filament, and    -   iv) optionally drawing and/or relaxing the resulting filament.

Preferably, the polyester fibers of the present invention are subjectedto single or multiple drawing in the course of their process ofproduction.

It is particularly preferable to produce the polyester fibers using apolyester produced by solid state condensation.

The polyester fibers of the present invention can be present in anydesired form, for example as multifilaments, as staple fibers orespecially as monofilaments.

The linear density of the polyester fibers according to the presentinvention can likewise vary within wide limits. Examples thereof are 100to 45 000 dtex and especially 400 to 7000 dtex.

Particular preference is given to monofilaments whose cross-sectionalshape is round, oval or n-gonal, where n is not less than 3.

The polyester fibers according to the present invention can be producedusing a commercially available polyester raw material. A commerciallyavailable polyester raw material will typically have a free carboxylgroup content in the range from 15 to 50 meq/kg of polyester. Preferenceis given to using polyester raw materials produced by solid statecondensation; their free carboxyl group content is typically in therange from 5 to 20 meq/kg and preferably less than 8 meq/kg ofpolyester.

However, the polyester fibers of the present invention can also beproduced using a polyester raw material which already comprises thenanoscale non-layered platelet-shaped filler. The polyester raw materialis produced by adding the filler during the polycondensation and/or toat least one of the monomers.

After the polyester melt has been forced through a spinneret die, thehot strand of polymer is quenched, for example in a quench bath,preferably in a water bath, and subsequently wound up or taken off. Thetakeoff speed is greater than the ejection speed of the polymer melt.

The polyester fiber thus produced is subsequently preferably subjectedto an afterdrawing operation, more preferably in a plurality of stages,especially to a two- or three-stage afterdrawing operation, to anoverall draw ratio in the range from 3:1 to 8:1 and preferably in therange from 4:1 to 6:1.

Drawing is preferably followed by heat setting, for which temperaturesin the range from 130 to 280° C. are employed; length is maintainedconstant, slight after-drawing is effected or shrinkage of up to 30% isallowed.

It has been determined to be particularly advantageous for theproduction of the polyester fibers of the present invention to operateat a melt temperature in the range from 285 to 315° C. and at a jetstretch ratio in the range from 2:1 to 6:1.

The takeoff speed is customarily 10-80 m per minute.

The polyester fibers of the present invention, as well as nanoscalenon-layered platelet-shaped filler, may comprise further auxiliarymaterials.

Besides the hydrolysis stabilizer already mentioned, examples of furtherauxiliaries are processing aids, antioxidants, plasticizers, lubricants,pigments, delusterants, viscosity modifiers or crystallizationaccelerants.

Examples of processing aids are siloxanes, waxes or long-chaincarboxylic acids or their salts, aliphatic, aromatic esters or ethers.

Examples of antioxidants are phosphorus compounds, such as phosphoricesters, or sterically hindered phenols.

Examples of pigments or delusterants are organic dye pigments ortitanium dioxide.

Examples of viscosity modifiers are polybasic carboxylic acids and theiresters or polyhydric alcohols.

The fibers of the present invention can be used in all industrialfields. They are preferably employed for applications where increasedwear due to mechanical stress is likely. Examples thereof are the use inscreens or conveyor belts. These uses likewise form part of the subjectmatter of the present invention.

The polyester fibers of the present invention are preferably used forproducing sheetlike structures, in particular woven fabrics used inscreens.

A further use for the polyester fibers of the present invention in theform of monofilaments concerns their use as conveyor belts or ascomponents of conveyor belts.

Particular preference is given to uses for the fibers of the presentinvention in screens which are wire screens and intended for use in thedry end of papermaking machines.

These uses likewise form part of the subject matter of the presentinvention.

The present invention further provides for the use of non-layeredplatelet-shaped particles selected from the group of inorganic oxides,hydroxides, carbonates, bicarbonates, nitrides and carbides, having athickness not more than 100 nm and an aspect ratio of not more than20:1, for producing fibers, especially monofilaments, having highabrasion resistance.

The examples which follow illustrate the invention without limiting theinvention in any way.

GENERAL OPERATING METHOD FOR INVENTIVE EXAMPLE 1

Polyethylene terephthalate (PET) and if appropriate hydrolysisstabilizer were mixed in an extruder, melted and spun through a 20 holespinneret die having a hole diameter of 1.0 mm at a feed rate of 488g/min and a takeoff speed of 31 m/min to form monofilaments, triplydrawn to draw ratios of 4.95:1, 1.13:1 and 0.79:1 and also heat-set in ahot air duct at 255° C. with shrinkage being allowed. The overall drawratio was 4.52:1. Monofilaments having a diameter of 0.25 mm wereobtained.

The PET used was a type having an IV value of 0.72 dl/g, to which 0.04%by weight of nanoscale Al₂O₃ of 50 nm had been added.

The hydrolysis stabilizer used was a carbodiimide (Stabaxol® 1, fromRheinchemie).

GENERAL OPERATING METHOD FOR COMPARATIVE EXAMPLES 1 AND 2

Monofilaments were produced as described in the operating method forInventive Example 1. Different PET raw materials were used but nonanoscale fillers. A type having IV value of 0.72 dl/g was used inComparative Example 1 and a type having IV value of 0.9 dl/g inComparative Example 2.

Fiber properties were determined as follows:

-   -   Tensile strength to DIN EN/ISO 2062    -   Breaking extension to DIN EN/ISO 2062    -   Hot air shrinkage to DIN 53843

Squirrel cage test: conducted using a rotatable metallic abrader havingmetal bars mounted on a drum rotating at a constant speed of rotation.The monofil was mounted on this abrader using a constant pretension. Thenumber of rotations to filament breakage is measured.

The table which follows summarizes the properties of the monofilaments.Hot air Fiber Tensile Breaking shrinkage Squirrel Example diameterstrength extension at 200° C. cage test No. [mm] [cN/tex] (%) (%)(cycles) Inv. 1 0.25 31.5 37.8 10.8 7503 Comp. 1 0.254 31.2 37.2 11.01249 Comp. 2 0.25 33.3 41.0 4.4 7342

While the invention has been described in detail, modifications withinthe spirit and scope of the invention will be readily apparent to thoseof skill in the art. In view of the foregoing discussion, relevantknowledge in the art and references including co-pending applicationsdiscussed above in connection with the Background and DetailedDescription, the disclosures of which are all incorporated herein byreference, further description is deemed unnecessary.

1. A fiber comprising aliphatic-aromatic polyester and non-layeredplatelet-shaped particles selected from the group of inorganic oxides,hydroxides, carbonates, bicarbonates, nitrides and carbides, having athickness in the range from 20 nm to not more than 100 nm and an aspectratio of not more than 20:1.
 2. The fiber according to claim 1 whereinthe polyester comprises structural repeat units derived from an aromaticdicarboxylic acid and an aliphatic and/or cycloaliphatic diol,especially polyethylene terephthalate repeat units alone or combinedwith other structural repeat units derived from alkylene glycols andaliphatic dicarboxylic acids.
 3. The fiber according to claim 1 whereinthe aliphatic-aromatic polyester has a free carboxyl group content ofnot more than 3 meq/kg.
 4. The fiber according to claim 3 comprising ahydrolysis stabilizer for blocking free carboxyl groups, preferably atleast one carbodiimide and/or at least one epoxy compound.
 5. The fiberaccording to claim 1 wherein the non-layered platelet-shaped particlesare not more than 80 nm and in particular from 20 to 60 nm in thickness.6. The fiber according to claim 1 wherein the non-layeredplatelet-shaped particles are oxides of magnesium, of calcium, ofstrontium, of aluminum, of gallium, of indium, of titanium, ofzirconium, of hafnium, of scandium, of yttrium, of silicon, ofgermanium, of tin or mixed oxides of these metals or semimetals.
 7. Thefiber according to claim 1 wherein the non-layered platelet-shapedparticles are carbonates of magnesium, of calcium or of strontium. 8.The fiber according to claim 1 wherein the non-layered platelet-shapedparticles are carbides of aluminum, of gallium, of indium, of silicon,of germanium or of tin.
 9. The fiber according to claim 1 wherein thenon-layered platelet-shaped particles are nitrides of aluminum, ofgallium, of indium, of silicon, of germanium or of tin.
 10. The fiberaccording to claim 1 wherein the non-layered platelet-shaped particlesare selected from the group consisting of aluminum oxide, aluminumnitride, silicon dioxide, zirconium dioxide, silicon carbide, siliconnitride, yttrium oxide or calcium carbonate.
 11. The fiber according toclaim 10 wherein the non-layered platelet-shaped particles are selectedfrom the group consisting of aluminum oxide or calcium carbonate. 12.The fiber according to claim 1 whose content of non-layeredplatelet-shaped particles is in the range from 0.1% to 5% by weight andpreferably in the range from 1% to 2% by weight, based on the mass ofthe fiber.
 13. The fiber according to claim 1 which, as well as thealiphatic-aromatic polyester, comprises from 0.1% to 5% by weight andpreferably from 0.5% to 2% by weight, based on the total mass of thepolymers, of polycarbonate.
 14. The fiber according to claim 1 which istransparent.
 15. The fiber according to claim 1 which is a monofilament.16. The fiber according to claim 1 incorporated into a screen orconveyor belt.
 17. The fiber according to claim 1 incorporated into awire screen intended for use in the dry end of papermaking machines. 18.A process for producing the fibers according to claim 1, the processcomprising the steps of: i) mixing polyester pellet with non-layeredplatelet-shaped particles selected from the group of inorganic oxides,hydroxides, carbonates, bicarbonates, nitrides and carbides having athickness in the range from 20 nm to not more than 100 nm and an aspectratio of not more than 20:1, ii) extruding the mixture comprisingpolyester and non-layered platelet-shaped particles through a spinneretdie, iii) withdrawing the resulting filament, and iv) optionally drawingand/or relaxing the resulting filament.
 19. The process according toclaim 18 wherein the polyester fiber is subjected to single or multipledrawing.
 20. The process according to claim 18 wherein the polyesterfiber is produced using a polyester produced by solid statecondensation.
 21. A process for producing the fibers according to claim1, the process comprising the steps of: i) feeding an extruder withpolyester pellet mixed before or during the polycondensation withpolyester pellet with non-layered platelet-shaped particles selectedfrom the group of inorganic oxides, hydroxides, carbonates,bicarbonates, nitrides and carbides, having a thickness in the rangefrom 20 nm to not more than 100 nm and an aspect ratio of not more than20:1, ii) extruding the mixture comprising polyester and non-layeredplatelet-shaped particles through a spinneret die, iii) withdrawing theresulting filament, and iv) optionally drawing and/or relaxing theresulting filament.
 22. In a process for making polyester monofilament,the improvement comprising providing high abrasion resistance byincorporating a non-layered platelet-shaped particles selected from thegroup of inorganic oxides, hydroxides, carbonates, bicarbonates,nitrides and carbides, having a thickness in the range from 20 nm to notmore than 100 nm and an aspect ratio of not more than 20:1.